High voltage liquid purifier and method



May 13, 1969 HIGH VOLTAGE LIQUID PURIF'IER AND METHOD Filed April 26, 1966 N. J. FELICI ET I Sheet Q M H HUN WWW 4.3.4, n NA I! lnl rm r IF I! II I! 2.7 V// v 8 s N.

May 13, 1969 J. FELlCl ETAL HIGH VOLTAGE LIQUID PURIFIER AND METHOD Filed April 26, 1966 Sheet AZZI VA ZZOVIIJ May 13, 1969 j F c ET AL 3,444,062

HIGH VOLTAGE LIQUID PURIFIER AND METHOD Filed April 26, 1966 Sheet United States Patent Office 3,444,062 Patented May 13, 1969 Int. Cl; 1301a 13/02 US. Cl. 204-180 18 Claims ABSTRACT OF THE DISCLOSURE A high voltage capacitive assembly having a static body of polar liquid permanently sealed in a fluid-tight container. Two electrically conductive membranes are disposed within the container and are provided with rigid backing members in direct contact with the membranes. The membranes are respectively permeable to positive and negative ions and serve as the electrodes for the assembly. Upon the application of a high potential across the membranes, an intense field is produced in the polar liquid, and selective migration of positive and negative impurity ions into the membranes takes places, bringing about a depletion of the impurityions in the liquid. The thus purified liquid exhibits an extremely high dielectric constant.

This invention relates to electrical apparatus and more particularly to such apparatus including a capacitive assembly which utilizes a fluid medium possessing a high dielectric constant.

There are many different types of electrical instruments and devices which, in use, involve the presence of an intense electric field between a pair of spaced electrodes having mutual capacitance. In apparatus of this character, there customarily is provided a substance which exhibits high resistivity, dielectric constant and breakdown voltage in the area of the intense field.

It has been known for many years to use polar liquids of high purity, obtained by subjecting the liquid to an ionexchange process, as the dielectric medium in various capacitive apparatus exposed to strong electric fields. The thus purified polar liquids initially possess remarkably high dielectric properties. However, these high initial characteristics are not-maintained but fall olI sharply during the operation of the apparatus because of contamination of the liquid from various sources. Extremely small amounts of contaminant, such as the minute concentrations of matter dissolved away from the inner surfaces of the glass or other vessel in which the liquid is contained, are suflicient to cause a sharp drop in the dielectric properties of the liquid, with the result that the advantages ex pected from its use in large measure are not realized.

Heretofore, attempts have been made to overcome this difficulty by circulating the dielectric liquid continually through purifying means during the operation of the apparatus. Such purification systems for the most part employed a closed flow circuit including a pump and regenerator apparatus external to the electrical apparatus. Among other disadvantages, the use of equipment of this type seriously complicated the construction of the apparatus, and the cumbersome character of the equipment rendered it entirely unsuitable in a great many applications, such as miniature instrumentation, for example, where small bulk, low weight, low power consumption and rugged simplicity are essential requisites.

Objects of this invention are to provide capacitive assemblies suitable for use in a variety of electrical apparatus under intense electric fields or voltage gradients which will have greatly improved operating characteristics due to a large and durable increase in the resistivity and dielectric characteristics of the dielectric medium across which the field is created.

A more specific object of the invention is to provide such capacitive assemblies which permit the prolonged use of polar fluids as the dielectric media, while at the same time,improving the simplicity of the assemblies.

Another object of the invention is to provide animproved method of purifying polar liquids.

Still another object of the invention is to provide new and improved electrical apparatus of the character indicated which is economical to manufacture and thoroughlygreliable in operation.

In accordance with a preferred embodiment of the invention, there is provided a capacitive assembly for highvoltage electrical apparatus which comprises a body of a suitable polar liquid or other fluid of the type which has high dielectric characteristics when the liquid is pure, but which exhibits comparatively lower resistivity characteristics when containing contaminant ions. A pair of high voltage electrodes are positioned in spaced capacitive relationship with each other on opposite sides of the body of flirid to create a strong electric field thereacross. These electrodes are made from ion-exchange materials of substantial electrical conductivity when dry. The material for one of the electrodes is selectively permeable to positive ions, while that for the other electrodes is selectively permeable to negative ions. The high voltage field across the fluid causes impurity ions, initially present in the liquid or" subsequently dissolved therein from a contaminant source such as the container walls, to migrate into and through the respective electrodes. With this arrangement, the fluid is brought to and continuously maintained in a state of extreme purity and correspondingly high resistive and dielectric characteristics.

The present invention may be considered an improvemei'lt in that described in copending US. patent application Ser. No. 387,286 filed Aug. 4, 1964 by Noel J. Felici arid Georges B. Briere. As more fully disclosed in that application, there is provided a capacitive assembly which includes three juxtaposed liquid-filled compartments in a container, the central compartment being separated from the side compartments by permeability-selective membranes which are respectively permeable to positive and negative ions. An electrode is disposed in each of the side compartments and is connected to one of the output terminals of a high voltage source to create the operating electric field. The central compartment is filled with a reasonably pure polar liquid, and the side compartments are filled with liquids which initially are identical with the liquid in the central compartment. In the operation of the assembly, selective migration of positive and negative impurity ions takes place from the central compartment through the corresponding permeability-selective membranes into the side compartments, bringing about a depletion of the impurity ions in the liquid in the central compartment. This purifying process is maintained continually over virtually indefinite periods.

Although capacitive assemblies of the character described in the above application have many important advantages, in several types of equipment the purification process will proceed with at least as high an efiiciency when the side compartments and the liquid in them are eliminated. In the resulting arrangement the permeability selective elements themselves are directly connected to the high voltage potentials and comprise the electrodes of the assembly. The desired purification of the liquid in the sin le remaining compartment proceeds, as it were, within the depth of the membranes themselves and at the interfaces, and the efiiciency of the resulting in-situ purification is 3 at least as high or higher than has been realized heretofore.

According to the present invention, therefore, the membranes themselves operate as selectively-permeable electrodes. The following are some of the considerations which are believed to contribute to an arrangement of this type:

1) Certain permeability-selective materials possess substantial electrical conductivity even in the dry state. Such conductivity is believed to be largely ionic in character, as later described in more detail, and illustratively corresponds to a resistivity of the order of 10 ohm-centimeters, with a capacitance of about picofarads per square centimeter or more for a membrane say 0.3 millimeter thick.

(2) Impurity ions become lodged within the pores or cells of the permeability-selective material, and eden though the thus lodged ions may retain their electrical charge, they are effectively disabled or neutralized because of the shielding (Faraday-cage) action of the coirductive walls of the cells in which they are imprisoned.

(3) The ability of the permeability-selective materials to accumulate and store ions is comparatively great, even when the material is in the form of a relatively thin membrane. Thus, ion-saturation ofthe permeability-seleciive electrodes is not a limiting factor for the practical lifetime of electrical apparatus in which a capacitive 'assembly according to the invention is embodied.

The present invention, as well as further objects and advantages thereof, will become more fully apparent from the following description of certain preferred embodiments, when read with reference to the accompanying drawings, in which:

FIGURE 1 is a partially schematic axial sectional view of a capacitive assembly having permeability-selective electrodes in accordance with one illustrative embodiment of the invention;

FIGURE 2 is a sectional view showing a permeabilityselective membrane in accordance with another illustrative embodiment;

FIGURE 3 is a sectional view similar to FIGURE 2 but showing a permeability-selective membrane in accordance With a further illustrative embodiment, together with certain cooperating parts;

FIGURE 3A is a fragmentary sectional view showing a modification of the embodiment of FIGURE 3; and

FIGURE 4 is a diagrammatic illustration which is useful in explaining certain ionic processes that are believed to take place in the permeability-selective electrodes.

The capacitive assembly illustrated by way of example in FIGURE 1 may form part of electrical apparatus of any of a wide variety of types in the general class of apparatus involving the presence of a strong electric field across a dielectric medium. The assembly is similar in its general layout to the Kerr cell assembly shown in FIGURE 2 of the above-identified application 'Ser. No. 387,286. A Kerr cell comprises one useful application of this invention, and furthermore it provides a convenient way of comparatively setting forth the distinctive features of this invention over the one disclosed in that application. Obviously, however, no limitation to Kerr cells is intended.

The assembly includes an annular body 1 of polytetrafluoroethylene or other insulating material. Two generally disc-like end members 8 and 8', which illustratively may be of the same material, are secured to the open ends of the body 1 by means of screws 4 and 4'. The members 8 and 8' have the outer edges of their inner surfaces respectively abutted against stepped shoulders 2 and 2' on the corresponding end of the body 1. The members 8 and8' further have annular flanges 10 and 10', respectively, which project inwardly to within a short distance from annular shoulders 3 and '3' on the inner protruding portion of the body 1. A circular semi-permeable membrane 12 is clamped between the flange 10 and the shoulder 3, while a circular semipermeable membrane 12 is similarly clamped between the flange 10 and the shoulder 3'. The

corner periphery of each of the shoulders 3 and 3 may be rounded slightly to reduce wear and damage to the membranes 12 and 12' in engagement therewith.

A pair of backing members 14 and 14 is respectively disposed against the outer faces of the semi-permeable membranes 12 and 12'. The backing members 14 and 14 are in the form of discs having rounded annular flanges 16 and 16, and each backing member is positioned between the corresponding membrane and the adjacent inner surface 11 or 11, of the end member 8 or 8. The flatend surfaces of the flanges 16 and 16' are seated against the inner surfaces 11 and 11, and the inwardlydirected surfaces of the backing members 14 and 14' are contoured to provide broad flat circular areas which seat against the corresponding areas on the outer surfaces of the membranes. The contour of the backing members also provides rounded peripheral areas which merge into the flanges 16 and 16 and seat against corresponding areas of the membranes. In the assembled condition, the backing members 14 and 14 cooperate with the peripheral clamping means in holding the respective membranes in substantial tension, with the inwardly directed surfaces of the membranes spaced apart to define a generally fiat circular compartment having an enlarged annular periphery. This compartment is filled with a body of polar liquid 21. For the introduction of the liquid, there is provided a filling aperture 5 which is formed in the annular body 1 and is fitted with a screw plug 7.

The backing members 14 and 14' firmly support the semi-permeable membranes 12 and 12 in stretched condition so that they will effectively withstand the electrostatic forces tending to move the membranes toward each other, as will be presently described. In the embodiment of FIGURE 1, the backing members serve the additional function of applying uniform voltages to the outer surfaces of the membranes. In this embodiment, therefore, the backing members are made of highly conductive metal and serve as ancillary electrodes or potential-distributing elements.

Two axially disposed electronic conductor rods 13 and 13' extend through central apertures in the end members 8 and 8'. The inner ends of the rods 13 and 13' make good electric contact with the centers of the backing members 14 and 14'. The rod 13 is electrically connected through a potentiometer 19 to a high voltage source schematically indicated at 20, and the rod 13 is similarly connected to ground. The source 20 illustratively comprises a high voltage electrostatic generator of the revolving charge-carrier type and is elfective to deliver a voltage of kilovolts or more, depending upon the particular application. In cases in which the assembly is part of a Kerr cell, there is provided a diametric passage 15 sealed from the liquid-filled compartment 21 by transparent sealing members (not visible in FIGURE 1). The sealing members transmit a narrow beam of light from a suitable source through the central part of the apparatus in a direction normal to the plane of the drawing so as to traverse the liquid 21. The liquid is selected to provide the requisite double refraction characteristics in addition to its other chemical and electrical properties referred to in greater detail hereinafter. If the strong D.C. field created by the generator 20 across the membranes 12 and 12', as indicated by the lines of force shown in dash lines, is modulated in accordance with a variable current, such as an audio-frequency current from a microphone, for example, the light beam will be modulated by the wellknown Kerr electro-optical process to produce a record on a film sound track, as explained in greater detail in the co-pending patent application referred to above.

In accordance with the present invention, the semipermeable diaphragms or membranes 12 and 12 operate as electrodes to maintain the high voltage field necessary for the operation of the apparatus, and the membranes simultaneously act to purify and continually maintain the polar liquid 21 or other dielectric medium in a high state from zero to a value of kilovolts per millimeter in about one hour. The resistivity of the polar liquid 21 first rises rapidly, and it then increases more slowly and finally attains a value which substantially equals its theoretical maximum. Simultaneously, the loss current through the condenser defined by the membranes 12 and 12 drops to a negligible value. The full voltage across the membrane-electrodes is then available to create an intense electric field through the liquid dielectric 21. These optimum operating conditions are retained for practically indefinite periods throughout the service life of the apparatus without it being necessary to renew or regenerate the liquid 21 at any time. The container 1 may therefore be permanently sealed to completely eliminate maintenance and service problems in this respect.

Some insight into the processes that take place within the device may be gained from a consideration of the highly schematized diagram of FIGURE 4. In this figure, there is shown a portion of the anodic or positive semipermeable membrane 12 with the adjacent portion of the body of polar liquid 21 at one side and the metallic voltage-distributing plate 14 at the other. The electrical field in the liquid 21 extends from the membrane 12 to the membrane 12 (FIGURE 1) and is indicated by the vector E. Impurity ions present in the liquid 21 are indicated as circled symbols and include both negatvie impurity ions (A") and positive impurity ions (C+). The negative impurity ions (or anions) are caused by the action of the field E to travel toward the membrane 12, whereas the positive impurity ions (cations) are propelled in the opposite direction toward the other membrane 12'.

The negative impurity ions (A*) are neutralized or inactivated on and in the membrane 12 by three more or less separate processes. All three processes are believed to occur concurrently in the operation of the apparatus.

The first process might be termed the Ion Discharge at Interface process. In this process an impurity anion (A-), upon reaching the liquid-membrane interface region indicated at 50 and contacting the inner'surface of the membrane 12, is immediately discharged 'in accordance with the reaction (A-) (AH-(e where (A) designates the neutral impurity atom and (e') designates an electron.

The second process is termed the Ion Transfer procto produce a neutral chlorine atom (Cl) at the interface 51.

The third process is termed lon Migration. In this case, an impurity anion (A-) that has not been discharged at the liquid-membrane interface 50 by the surface-discharge process succeeds. in traversing the full thickness of the membrane and'is discharged at the op- 6 posite interface 51 by the reaction (A-) (A)+(e-), leaving an impurity atom (A) at the interface 51.

The threefold process may be summarized as follows. The surface-discharge action is similar to ordinary electrolysis and results in a deposit of solid matter at the liquidamembrane interface and some evolution of gas. The ion-transfer process, which statistically appears to be the major process occurring in the device, results in a deposit of undischarged impurity ions which are lodged within the pores of the membrane. These accumulated undischarged, ions are effectively prevented from exerting further influence because of the conductive character of the membrane, each cell or pore thereof acting as a minute Faraday cage which shields any undischarged ion that may be lodged therein. Thus, the undischarged carriers within the membrane are incapable of generating an electrical field at the interface 50, in contrast to what occurs in the case of metallic electrodes wherein injected charge carriers create intense parasitic fields that are responsible for comparatively large losses. It should be noted in this connection that any metallic positive charge carrier atoms that might tend to be injected from the voltage-distributing plate 14 are prevented from penetrating the membrane 12 because of the relative impermeability of the membrane with respect to such atoms. These positive atoms remain at the interface 51, where they are promptly neutralized by anions which may be either impurity ions (A-) in the final phases of migration through the membrane or membrane (e.g. chlorine) ions (01-) similarly approaching the end of their migration. This last-described process is schematically indicated in the lower left portion of FIGURE 4 and might be termed Injected Carrier Neutralization.

It will thus be apparent that in the steady operating state of the apparatus the membrane 12 has an accumu lation of neutral impurity atoms at its inner surface (and also at its outer surface if a metallic voltage-distributing plate is used). The membrane also has an accumulation of electrically charged, though effectively disabled, impurity ions which are trapped in its internal cells.

The storage capacity of a semi-permeable membrane for accumulating impurity atoms and ions in the manner just described is extremely great, and a considerable period will lapse before the membrane approaches a state of saturation under reasonable operating conditions. This storage capacity illustratively is of the order of at least 10 ion-grams per gram of the membrane material. The impurity ion concentration in a commercially pure polar liquid at the time it is initially introduced into the device customarily is no higher than about l0 ion-grams per liter. Further, the combined rate of dissolution of positive and negative impurities from the walls of the container into the liquid can be estimated to be a maximum of about 10* ion-grams per liter per hour. Considering a body of polar liquid having a thickness or depth h which is enclosed between two semi-permeable membranes of thickness 2 and specific gravity approximately equal to unity, the time lapse before the two membranes become saturated with impurities will be If e is equal to 0.3 millimeter and h is equal to 6 milli meters, the time T will be 100,000 hours.

Accordingly, assuming reasonable values for the initial purity of the polar liquid and for the rate of dissolution of impurities therein from the container walls and other contaminating sources, the time required for the membranes to approach saturation will generally exceed the normal lifetime of the apparatus. Also, in many cases the membranes may be replaced after a prolonged period of operation, should this be desirable.

In the operation of the apparatus, the membranes are exposed to very strong electrostatic forces which tend to move them inwardly toward each other. Various expe 7 dients may be used according to the invention for counter-- acting those forces and ensuring prolonged operation of the apparatus without structural breakdown.

As an illustration, in the FIGURE 1 embodiment the membranes 12 and 12' are bonded to the metal plates 14 and 14' by an electrically conductive adhesive which is impervious to the dissolving action of the liquid. Such an adhesive may comprise a polymerizable resin having a highly divided conductive substance admixed therein. In some cases, the conductive substance comprises a powder metal, such as silver or platinum, for example, while in other situations powder graphite is employed, preferably in a proportion of about from to 50% by weight. The mixture of monomer and conductive particles is placed between the membrane and the metal plate with a suitable curing or polymerizing agent, and after assembly the adhesive composition is allowed to polymerize in situ.

Instead of or in addition to adhesive, the body of liquid 21 may be introduced and maintained under substantial pressure, thereby urging the membranes 12 and 12 against the metal plates 14 and 14 with sufficient force to counteract any tendency toward separation under the action of the electrostatic forces.

The membranes 12 and 12 also may be of substantially increased thickness and hence stiffness, to thereby contribute to the desired mechanical rigidity. Thus, whereas several types of semi-permeable membranes useful with the invention are fabricated with a thickness of about 0.3 millimeter or less, in other cases the membranes are provided with a thickness which ranges from about 0.5 millimeter to about 2.0 millimeters or even higher. The increased thickness is further advantageous in that it provides increased ion storage capacity, as will be understood from the earlier explanations given herein.

A further form of construction for the permeabilityselective membranes is schematically shown in FIGURE 2. In this figure, the membrane comprises a body 22 of permeability-selective ion-exchange material and a reinforcement 24 imbedded therein. The reinforcement 24 is in the form of a grate or wire mesh made from a suitable non-corrodable, electrically conductive metal, such as an iridium tantalum alloy, platinum, or the like. The body 22 is molded around the metal wire mesh 24. The wire mesh serves as the potential-distributing member for the electrode, and for this purpose a conductor 23 is soldered to the center of the mesh and extends outwardly from the membrane assembly for connection to the high voltage source. In a construction of this type, the metal backing plates 14 and 14 of FIGURE 1 may be omitted or replaced with backing members of insulating material.

In the embodiment of FIGURE 3, parts corresponding in function to parts of FIGURE 1 have been identified by the same reference numbers together with the prefix 3. In the FIGURE 3 embodiment, there is provided an annular body 31, an end member 38 of flattened construction and a backing member 44 of insulating material. The backing member 44 is centrally supported by a post or stud 54 which is fitted in a centering hole in the member 38. A semi-permeable conductive membrane 42 is stretched across the inner surface of the backing member 44 and has its peripheral edge clamped between the annular surface of a ledge 33 on the body 31 and the flat under surface of a ring 56. The ring 56 is fabricated from a highly conductive metal and is retained in position by the end member 38.

A metallic conductor rod or wire 43 is electrically com nected to the ring 56 and protrudes from the body 31 for connection to a high voltage source (not shown in FIG- URE 3). The electrode-membrane 42 is bonded to the adjacent surface of the backing member 44 by a layer of electrically insulating adhesive composition 58 which is polymerized in situ. In some cases, the membrane 42 preferably is of the type which. includes a wire mesh reinforcement which is connected to the conductor 43. Thus, in the modification shown in FIGURE 3A, the semi-permeable membrane 62 incorporates a conductive wire mesh element 64. A peripheral section of the membrane 62 is cut away to expose the wire mesh element so that the element will make good electrical contact with the conductive clamping ring 56.

Each of the illustrated embodiments of the invention utilizes two semi-permeable membranes of opposite selectivity characteristics, as has been described with reference to FIGURE 1. It should be observed, however, that the purifying actions of the two membranes are largely independent of one another, so that in other embodiments the semi-permeable membrane means may be of a single selectivity type, i.e., an anodic membrane or a cathodic membrane. Such arrangements may be employed in cases where a polar dielectric liquid is to be stripped of only one type of contaminant, where the liquid is in relative motion so as to be successfully exposed to the action of an anodic selective membrane and a cathodic selective membrane, and for various other applications.

The polar liquids which are used in the illustrated embodiments of the invention may include substantially any organic polar liquid. The liquids preferably are selected to have a comparatively low ionization factor so that the theoretical specific resistivity, which is directly related to the. ionic dissociation constant, is high. Nitrobenzene, nitrotoluene, acetone and acetonitrile are examples of suitable liquids which may be employed with good effect.

The permeability-selective membranes may be made from any suitable ion-exchange materials having adequate conductivity. Preferably, the membranes exhibit a resistivity which is not higher than about 10 ohm-centimeters in the dry or dehydrated state.

One of the outstanding advantages of the invention is the elimination of space-charge effects resulting from the local build-up of ions at the liquid-metal interface of conventional metallic electrodes. Heretofore, such spacecharge action often produced non-homogeneous field distributions in the liquid in the vicinity of the electrode surfaces, and this resulted in field distortion and high local losses by charge-injection and the Joule effect. These difliculties have limited the field strengths with which liquid dielectric media could be used in prior apparatus of this general type. In the present invention, the character of the electrode material prevents any accumulation. of ions and resulting space-charge adjacent the electrode surfaces and provides a substantial increase in the permissible field strengths. 4

Certain advantageous embodiments of the invention also include a method of producing polar liquids having high purity and correspondingly high electrical characteristics, which method comprises the steps of maintaining the liquid in contact with spaced electrodes respectively made of positive and negative ion-exchange materials of substantial electric conductivity, and applying, preferably gradually, a unidirectional potential difference across the electrodes.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. In high voltage electrical apparatus, an electric field producing assembly comprising, in combination, fluid retaining means, a body of fluid sealed in said retaining means, said fluid exhibiting high resistivity and dielectric characteristics but having comparatively lower resistivity and dielectric characteristics when containing contaminant ions, said fluid retaining means including at least one ionpermeable element exposed to said fluid, said element being fabricated from selectively permeable ion exchange material of substantial electrical conductivity when dry, and electronic conductor means in contact with said ion permeable element for applying a high predetermined po-= tential to said element to create a strong electrical field in said fluid, said electrical field driving contaminant ions in the fluid into said element to maintain the fluid in a condition of high purity with high resistivity and dielectric characteristics,

2. Apparatus of the character set forth in claim 1, in which said ion-permeable element --has a resistivity which is not in excess of about ohm-centimeters when dry, the impurity of the fluid in said retaining means prior to the application of said potential being not greater than about 10* ion-grams per liter.

3. In high voltage electrical apparatus, an electric field producing assembly comprising, in combination, liquid retaining means, a body of polar liquid sealed in said retaining means, said liquid exhibiting high resistivity and dielectric characteristics but having comparatively lower re sistivity and dielectric characteristics when containing contaminant ions, said liquid retaining means including at least one ion-permeable element exposed to said liquid and an electrically conductive backing member in direct contact with said element, said element being fabricated from selectively-permeable ion exchange material, and means for applying a high predetermined potential to said element to create a strong electrical field in said liquid, said electrical field driving contaminant ions in said liquid into said element to maintain the liquid in a condition of high purity with high resistivity and dielectric char= acteristics.

4. In high voltage electrical apparatus, a capacitive assembly comprising, in combination, fluid retaining means, a body of fiuid sealed in said retaining means, said fluid exhibiting high resistivity and dielectric characteristics but having comparatively lower resistivity and dielectric characteristics when containing contaminant ions, said fluid retaining means including a pair of ion-permeable elements and means for mounting said elements in spaced capacitive relationship with each other, each of said ele ments having a surface area exposed to said fluid and being fabricated from ion exchange material of substantial electrical conductivity when dry, and electronic conductor means in contact with said ion permeable elements for applying a high predetermined potential to said elements to create a strong electrical field in said fluid, said electrical field maintaining the fluid in a condition of high purity with high resistivity and dielectric characteristics.

5. In high voltage electrical apparatus, a capacitive assembly comprising, in combination, fluid retaining means, a body of fluid sealed in said retaining means, said fluid exhibiting high resistivity and dielectric characteristics but having comparatively lower resistivity and dielectric characteristics when containing contaminant ions, said fluid retaining means including a pair of ion-pen meable elements and means for mounting said elements in spaced capacitive relationship with each other, each of said elements having a surface area'exposed to said fluid and being fabricated from ion-exchange material of sub stantial electrical conductivity when dry, one of said elements being selectively permeable to positive ions and the other of said elements being selectively permeable to negative ions, and electronic conductor means in contact with said ion permeable elements for applying a high predetermined potential to said elements to create a strong electrical field in said fluid, the fluid in said retaining means being of reasonable purity prior to the application of said potential but containing contaminant ions, said electrical field driving contaminant ions in said fluid into said elements to maintain the fluid in a condition of high purity with high resistivity and high dielectric characteristics.

6. In high voltage electrical apparatus, a capacitive assembly comprising, in combination, liquid retaining means, a body of polar liquid sealed in said retaining means, said liquid exhibiting high resistivity and dielectric characteristics but having a comparatively lower resistivity and dielectric characteristics when containing contaminant ions, said liquid retaining means including a pair of ion-permeable electrodes and means for mounting said electrodes in spaced capacitive relationship with each other, each of said electrodes having a surface area exposed to said liquid and being fabricated from ion exchange material of substantial electrical conductivity when dry, one of said electrodes being selectively per= meable to positive ions and the other of said electrodes being selectively permeable to negative ions, and means for applying a high predetermined potential to said electrodes to create an intense electrical field in said liquid, said electrical field maintaining the liquid in a condition of high purity with high resistivity and dielectrc characteristics.

7. Apparatus of the character set forth in claim 6, wherein said ion-permeable electrodes comprise relatively thin membranes which respectively exhibit anodic and cathodic permeability-selective properties.

8. Apparatus of the character set forth in claim 6, wherein each of said electrodes comprises a reinforcing wire mesh of electrically conductive material, said potential applying means including conductor means connected to said mesh for applying said potential thereto.

9. In high voltage electrical apparatus, a capacitive assembly comprising, in combination permanently sealed, liquid retaining means, a static body of liquid in said retaining means, said liquid exhibiting high resistivity and dielectric characteristics but having comparatively lower resistivity and dielectric characteristics when containing contaminant ions, said liquid retaining means including a pair of ion-permeable elements and backing means for mounting said elements in spaced capacitive relationship with each other, each of said elements having a surface area exposed to said liquid and being fabricated from ion exchange material, one of said elements being selectively permeable to positive ions and the other of said elements being selectively permeable to negative ions, and electronic conductor means for applying a high predetermined potential to said elements to create a strong electrical field in said liquid, said electrical field maintaining the liquid in a condition of high purity with high resistivity and dielectric characteristics.

10. Apparatus of the character set forth in claim 9, comprising means for clamping each of said ion-perme able elements to said backing means to maintain said ele= ments in stretched condition.

11. Apparatus of the character set forth in claim 9, said backing means comprising a pair of backing members having surface areas in contact with said ion-per= meable elements, and means for bonding said surface areas to said elements. I

12. Apparatus of the character set forth in claim 11, wherein each of said backing members is of electrically conductive material, said potential applying means in= cluding conductor means connected to said backing members.

13. In high voltage electrical apparatus, a capacitive assembly comprising, in combination, permanently sealed liquid retaining means, a body of static polar liquid under substantial pressure in said retaining means, said liquid exhibiting high resistivity and dielectric characteristics but having comparatively lower resistivity and dielectric char: acteristics when containing contaminant ions, said liquid retaining means including a pair of ion-permeable electrode membranes, an electrically conductive backing member for each of said membranes and clamping means for holding each said membrane in direct contact with its backing member and for maintaining said membranes in spaced capacitive relationship with each other, each of said membranes having a surface area exposed to said liquid and being fabricated from ion exchange-material, one of said membranes being selectively permeable to positive ions and the other of said membranes being selectively permeable to negative ions, and voltage means for applying a high predetermined potential to said mem= 1 l. branes to create a strong electrical field in said liquid, said electrical field driving contaminant ions in said liquid into said membranes td maintain the liquid in a condition of high purity with high resistivity and high dielectric characteristics.

14. In a method of producing a polar liquid having high purity, resistivity and dielectric characteristics, the steps of maintaining a body of liquid in contact with a pair of spaced elements respectively fabricated from positive and negative ion-exchange material of substantial elec trical conductivity, said liquid exhibiting high resistivity and dielectric characteristics when substantially pure but. having a comparatively lower resistivity and dielectric characteristics when containing contaminant ions, and applying a high unidirectional potential difference to said elements by electronic conductor means in direct contact therewith to create an intense electric field in said liquid and thereby maintain the liquid in a condition of high purity with high resistivity and high dielectric character-= istics.

15. In a method of producing a polar liquid having high purity, resistivity and dielectric characteristics, the steps ofamaintaining a body of polar liquid in contact with a pair of spaced electrodes respectively fabricated from positive and negative ion-exchange material, said liquid exhibiting high resistivity and dielectric characteristics when substantially pure but having comparatively lower resistivity and dielectric characteristics when containing contaminant ions, and applying a large unidirectional potential difference of at least about one hundred kilovolts between said electrodes to create an intense electric field in said liquid and thereby maintain the liquid in a condition of high purity with high resistivity and high dielectric characteristics.

16. In a method of producing a polar liquid having high purity, resistivity and dielectric characteristics, the steps of, maintaining a body of polar liquid in contact with a pair of spaced elements. respectively fabricated from positive and negative ion-exchange material of substantial electrical conductivity, said liquid exhibiting high resistivity and dielectric characteristics but having comparatively lower resistivity and dielectric characteristics when containing contaminant ions, and applying a large unidirectional potential difference in gradually increasing increments between said elements by electronic conductor means in direct contact therewith to create an intense electric field in said liquid and thereby maintain the liquid in a condition of high purity with high resistivity and high dielectric characteristics.

17. In a method of the character set forth in claim 14, the step of permanently sealing said body of liquid and the ion-exchange elements in an enclosed container.

18. In a method of the character set forth in claim 16, said potential difference being gradually increased from zero to about 10 kilovolts for each millimeter between said electrodes during the first hour following the application of said potential therebetween.

Spiegler: Principles of Desalination, 1966, p. 209. Hampel: Encyclopedia of Electrochemistry, 1964, Reinhold Pub. Corp., pp. 726-729.

JOHN H. MACK, Primary Examiner.

A. C. PRESCOTT, Assistant Examiner.

US. Cl. X.R. 

